Role of Distribution Switch

Question

Hello all,
Can any one explain me what is the role of distribution switch in netwok environment? How the network should be designed proper having it.
My confusion is, having distribution switch in network, should we configure layer3 interfaces on distribution or on core ? how the connected users at access layer switch should communicate with other vlans ? does intervlan routing should be enabled on distribution switch or at core ? what should be the gateway configured for access layer switches or for end users ?
Regards,

Answer 1

As the others have said the core is generally used to simply interconnect your distribution switches, usually using L3 routed links ie. no need for vlans between distro and core.
That said you seem to be talking about a building rather than a campus setup. In a campus set you can have multiple buildings with access switches per floor connecting to a distro pair that do inter vlan routing for the buildings vlans and then each distro pair is connected to core set of switches that route between buildings. This is a standard Cisco 3 tier design but within a single building it might not be the best approach.
In a single building design, as Reza mentioned, a more common design is a collapsed distribution/core where the same pair of switches do both. Each floor really doesn't need a distribution switch unless there is an abnormally high amount of traffic between vlans on the same floor which is generally not the case.
So your access switches on each floor connect back to core/disto pair of switches which handle all the inter vlan routing. As devils advocate mentioned. you can extend L3 back to the access layer but there are limitations with this and with the advent of VSS/MEC on the 6500s and MEC on the 3750s a lot of the advtantage of running L3 to the access layer has gone, and you still get the flexibility that L2 can give you ie. the ability to have a vlan on multiple access switches.
Ideally you do not want servers connecting directly into the core/distro pair (and certainly not the core if you had a dedicated core pair of switches). You would want a separate pair of switches for the servers that then connect back to the core/distro pair. But this often comes down to cost and you often see servers connected to the core/distro pair.
If it is one building i would use the 6500s as a core/distro pair and run MEC from the switches on each floor back to the 6500s. Inter vlan routing would be done on the 6500s, again with the proviso that most of the traffic is between clients on the floors and servers and not between clients and other clients on the same floor.
There is no need to have distribution switches per floor. If you do then be aware that is in effect a L3 routed access layer and the major restriction is that if you have vlan/IP subnet on one switch you cannot then have the same vlan/IP siubnet on another switch on a different floor.
Jon